The present invention relates to a process for preparing sulfonate salts via alkaline hydrolysis of the corresponding sulfonyl chlorides.
The conventional method for obtaining a sulfonate salt from a sulfonyl chloride consists in carrying out the hydrolysis of the sulfonyl chloride using inexpensive bases, such as alkali metal or alkaline earth metal carbonates or hydroxides, e.g. sodium hydroxide. However, the literature includes only a few cases of alkaline hydrolysis of sulfonyl chloride by this kind type of bases: mention may be made, among these rare examples, of R. N. Haszeldine (J. Chem. Soc., 2901 (1955)), who describes a quantitative alkaline hydrolysis of trifluoromethanesulfonyl chloride by 15% sodium hydroxide, i.e. by a sodium hydroxide solution with a relatively low concentration.
It should be noted that the hydrolysis of a sulfonyl chloride, and in particular of a (per)fluorinated sulfonyl chloride, is generally difficult to carry out, especially because of the covalent nature of the SO2xe2x80x94Cl bond, and in view of the fact that these substrates are generally better oxidizing agents than electrophiles. In this respect, it should actually be emphasized that similar compounds, such as sulfuryl chloride SO2Cl2, are commonly used as chlorinating agents. Generally, sulfonyl chlorides are therefore often not very reactive with respect to the hydrolysis reaction.
Consequently, the problem encountered during the alkaline hydrolysis of a sulfonyl chloride is as follows: the hydrolysis reaction of the sulfonyl chloride is a reaction which, on the one hand, intrinsically has a significant exothermic nature and which, on the other hand, is characterized by significant inertia, due to the fact that the reactants are present in two, separate phases, which accentuates the exothermicity of the reaction. This inertia does not give rise to any complication during the hydrolysis of small amounts and/or with dilute alkaline solutions, such as those described in the literature; however, it raises real safety problems as soon as attempts are made to carry out the reaction with higher concentrations of base and/or on industrial amounts: this is because the inertia of the reaction then leads to a buildup of sulfonyl chloride during the reaction which can represent up to 20% of the amount of sulfonyl chloride introduced and which, in conjunction with the high intrinsic exothermicity of the hydrolysis reaction, can lead to runaway of the reaction.
To avoid such problems, the only currently existing solution consists in carrying out the alkaline hydrolysis by means of a dilute hydroxide solution, which involves removing the water by additional distillation stages, harmful in terms of industrial productivity.
The aim of the present invention is specifically to provide a method for the preparation of sulfonate salts which are simultaneously inexpensive, fast and reliable, by carrying out the alkaline hydrolysis of a sulfonyl chloride with a concentrated basic solution, but while avoiding the problem of buildup of the sulfonyl chloride due to the inertia of the reaction.
More specifically, the resent invention relates to a process for preparing an alkali metal or alkaline earth metal sulfonate salt corresponding to the anion of general formula (I):
Rxe2x80x94CF2xe2x80x94SO331xe2x80x83xe2x80x83(I),
wherein R is:
(a) a hydrogen atom;
(b) a halogen, preferably a light halogen (that is to say, with an atomic number at most equal to that of chlorine), and more preferably fluorine;
(c) an alkyl chain optionally substituted by one or more halogen atom(s);
(d) an alkenyl chain optionally substituted by one or more halogen atom(s);
(e) an aryl group which is optionally substituted by one or more halogen atom(s) and which can comprise one or more heteroatoms;
(f) an arylalkyl group optionally substituted by one or more halogen atom(s), it being possible for the aryl group to comprise one or more heteroatoms; or
(g) a sulfonyl heavy halide group,
with it being possible for R, when it is a group as defined in (c), (d), (e) and (f), to be substituted by a sulfonyl heavy halide group,
said sulfonate salt being obtained from a sulfonyl chloride of general formula (II)
Rxe2x80x94CF2xe2x80x94SO2Cl
wherein R is as defined above,
said process comprising at least one stage of alkaline hydrolysis of the sulfonyl chloride (II) in the presence of at least one compound acting as a phase transfer agent.
The R group present in the sulfonyl chlorides employed in the process of the invention is preferably an electron-withdrawing group, that is to say a radical with a "sgr"p value generally greater than 0, preferably greater than 0.1 and advantageously at least equal to 0.5.
R is advantageously a fluorine atom or a perfluoroalkyl radical Rf optionally substituted by a sulfonyl heavy halide group.
Within the meaning of the invention, a sulfonyl heavy halide group refers to a group carrying a sulfonyl halide functional group or a halogen and chlorine or bromine and preferably chlorine and for which the carbon atom adjoining the sulfur atom is perhalogenated by halogens with an atomic number at most equal to that of chlorine and is preferably perfluorinated. This group can have from 1 to 10 carbon atoms.
Thus, the claimed process s especially suitable for preparing alkali metal or alkaline earth metal sulfonate salts which exhibit at least one, indeed even two, sulfonyl group(s), the carbon atom(s) adjoining the sulfur atom(s) being perfluorinated.
These bisulfonate compounds can be useful in particular for preparing polymeric compounds or alternatively cyclic compounds, when the number of linking units separating the two sulfonate functional groups is 2, 3 or 4. The linking units which separate the two sulfonate functional groups are advantageously CF2 linking units.
Furthermore, it should be pointed out that the, carbonaceous chains present in the sulfonyl chlorides employed in the process of the invention are preferably saturated chains, so as in particular to avoid phenomena of untimely polymerization. Furthermore, the sulfonyl chlorides employed in the process of the invention generally comprise a total carbon atom number advantageously of less than 30.
Within the meaning of the present invention, the term xe2x80x9cphase transfer agentxe2x80x9d denotes a compound capable of compensating for the inertia of the hydrolysis reaction and of preventing the problem of the buildup of the sulfonyl chloride due to the fact that the reactants are found in two separate phases.
This phase transfer agent may be either of cryptant type, such as crown ethers, or of onium type, or an alcohol.
Thus, according to a first aspect of the invention, the role of phase transfer agent is played by a phase transfer agent of onium cation type.
Oniums are compounds with names, in the nomenclature, comprising the sequence of letters xe2x80x9coniumxe2x80x9d as affix, generally as suffix. They are semimetallic compounds, in particular from the nitrogen column and from the sulfur column, which are sufficiently substituted to carry a positive charge. Thus, the atoms from the nitrogen column, when they are substituted four times by a hydrocarbonaceous radical, constitute oniums.
Thus, quaternary ammoniums or quaternary phosphoniums can be used as phase transfer agent.
Sulfoniums (tertiary in their case) themselves also constitute phase transfer agents, but they are less advantageous, since they are relatively more unstable than the others.
The oniums used as phase transfer agent are known to a person skilled in the art.
The most commonly used are tetraalkylammoniums and tetraalkyl- or tetraphenylphosphoniums. The latter exhibit, however, the disadvantage of being relatively expensive.
The preferred phase transfer agents among said, onium cations are tetraalkylammonium comprising saturated, unsaturated or aromatic hydrocarbonaceous chains comprising a total of 4 to 28 carbon atoms, preferably of 4 to 16 carbon atoms.
To avoid xcex2-elimination reactions, the most widely used onium is tetramethylammonium, although it is relatively unstable from approximately 150xc2x0 C.; mention may also be made of benzyltrimethylammonium.
The onium cation is preferably employed in an amount representing from 1 to 20 mol % with respect to the total number of sulfonyl chloride functional group(s) present on the compound of formula II, more preferably from 1 to 5 mol %.
According to a second aspect of the invention, which is a preferred embodiment, an alcohol, in particular a linear or branched and aliphatic or aromatic alcohol, comprising from 1 to 10 carbon atoms, preferably more than 2 carbon atoms, is used as phase transfer agent, the most preferably used alcohol being selected from isopropanol, ethanol, benzyl alcohol, isobutanol, n-propanol and sec-butanol.
In fact, any alcohol is suitable as phase transfer agent according to the present invention, insofar as it is incapable of participating in side reactions, in particular in the formation of an ether in a sufficient amount to threaten the reliability of the process.
In this respect, it is surprising to find that a primary or secondary alcohol can be employed in the basic hydrolysis process of the invention. This is because the sulfonyl chloride employed is generally a better oxidizing agent than electrophile, which should lead to the oxidation of the alcohol employed, very particularly in the context of the use of perfluorinated sulfonyl chlorides, the oxidizing nature of which is very pronounced. Furthermore, it should be emphasized that, among the alcohols preferably employed, isopropanol is known as being a good reducing agent.
Whatever its nature, the alcohol used is preferably employed in a proportion of 0.05 to 1 molar equivalent with respect to the number of sulfonyl chloride functional group(s) present on the compound of formula II, more preferably in a proportion of 0.1 to 0.2 molar equivalent.
Said alcohol used as phase transfer agent can optionally be partially present in the form of the alkoxide ion in the basic hydrolysis medium.
The term xe2x80x9calkaline hydrolysisxe2x80x9d is understood to denote, within the meaning of the present invention, hydrolysis by means of a basic solution of an alkali metal or alkaline earth metal hydroxide or of a solution of carbonate salts.
The alkali metal or alkaline earth metal hydroxide solutions which are very particularly suitable for the present invention are solutions of a metal hydroxide of general formula III:
(M)(OH)nxe2x80x83xe2x80x83(III),
where
M is an alkali metal or alkaline earth metal, and preferably an alkali metal; and
n is an integer:
equal to 1 in the case where M is an alkali metal,
equal to 2 in the case where M Is an alkaline earth metal, in a solvent of hydroxylated type, the preferred solvent being water, a preferred alkali metal hydroxide solution being an aqueous sodium hydroxide solution.
The solutions of carbonate salts according to the present invention are solutions of a metal carbonate of general formula (IV):
(M)n(CO3)xe2x80x83xe2x80x83(IV),
where
M is an alkali metal or alkaline earth metal, preferably an alkali metal or magnesium, and advantageously sodium; and
n is an integer:
equal to 1 in the case where M is an alkaline earth metal,
equal to 2 in the case where M is an alkali metal, in a solvent of hydroxylated type, the preferred solvent being water.
As emerges from the examples presented below, the alcohol acts, like the onium salt, as a phase transfer agent between the alkaline solution and the sulfonyl chloride, even if the nature of this phase transfer remains to be specifically defined. Measurements of heats of reaction given off during alkaline hydrolyses carried out in the presence of an alcohol in any case undoubtedly reveal a sharp reduction in the buildup of the sulfonyl chloride during the reaction in comparison with measurements carried out in the absence of phase transfer agent: the presence of alcohol leads to a marked decrease in the delay observed in the evolution of the heat of reaction, that is to say a substantial increase in the rate of the alkaline hydrolysis reaction.
The preferred process according to the invention comprises a stage of gradual addition of sulfonyl chloride at atmospheric pressure to a mixture comprising at least:
said alkaline solution of hydroxide or of carbonate, and
said phase transfer agent composed of a compound of cryptant type, of a compound of onium salt type or of an alcohol.
Preferably, the alkaline solutions are aqueous solutions and are employed at concentrations of greater than 20% by mass, which makes it possible to eliminate the stages of distillation of water. Furthermore, in order to be able to carry out correct stirring, this concentration, which should not be too high in order to avoid an excessively high viscosity, is more preferably between 20 and 30% by mass.
In order to carry out a quantitative reaction, whatever the nature of the base used, the base is generally employed in an amount close to the stoichiometry of the reaction, that is to say in an amount of the order of two molar equivalents with respect to the number of sulfonyl chloride functional group(s) present on the compound of formula II, advantageously in a proportion of 1.8 to 2.5 molar equivalents, and preferably in an amount equal to 2 molar equivalents, with respect to the number of sulfonyl chloride functional group(s) present.
Whether an alcohol or an onium salt is used, it may be considered that the presence of the phase transfer agent makes it possible to decrease the duration of the hydrolysis reaction by approximately 50%, which, first, improves the efficiency of the process but also makes it possible to operate under enhanced conditions of safety by preventing the problems related to the buildup of the sulfonyl chloride. Be that as it may, as a result of the high intrinsic exothermicity of the reaction, the hydrolysis can be carried out while cooling the reaction medium using, for example, an ice bath. This is because it is generally preferable for the temperature of the reaction medium to be maintained between xe2x88x9210xc2x0 C. and 50xc2x0 C. during the alkaline hydrolysis. It is advantageously preferable for this temperature not to exceed 30xc2x0 C. In the specific case of the use of CF3SO2Cl in the alkaline hydrolysis stage, it is furthermore preferable for this temperature to remain. below 20xc2x0 C., in particular as a result of the low boiling point (29xc2x0 C.) of this compound. However, if it is desired to implement the process of the invention at temperatures greaer than or equal to the boiling point of the sulfonyl chloride used, it is possible to carry out the reaction at a pressure greater than atmospheric pressure, for example in a closed chamber, and generally, in this case, at the autogeneous pressure of the reaction medium at the temperature at which it is desired to operate.
However, it should be clearly emphasized that the limitation on the rise in the temperature is generally due essentially to the presence of a phase transfer agent, which limits the phenomena of buildup of the sulfonyl chloride, very particularly in the case of the use of large amounts of reactant.
Furthermore, it should also be noted that the specific presence of the phase transfer agent makes it possible to carry out the process of the invention on an industrial scale without risk of overheating or of runaway of the reaction. Thus, the amounts of sulfonyl chloride employed in the process of the invention can, in the general case, reach amounts of greater than 1000 mol, indeed even greater than 5000 mol.
It should also be noted that the process of the invention lends itself to a continuous embodiment.
According to one aspect of the invention, the alkaline hydrolysis process makes It possible to obtain said sulfonate salt in solution, preferably in aqueous solution, for example for a direct use in situ of said salt as reaction intermediate, in particular for the synthesis of the corresponding sulfonic acid, these operations coming within the competence of a person skilled in the art.
According to another aspect of the invention, the process of preparation of the sulfonate salt makes it possible to obtain the salt in the solid form, in particular by selective precipitation and/or by concentrating to dryness, for example for an optionally subsequent use of said salt as reaction intermediate, in particular for the synthesis of the corresponding sulfonic acid, in a way also known per se.